1. Field of the Invention
The invention relates to a method of fabricating a semiconductor device such as LSI, and more particularly to chemical mechanical polishing (CMP) in such a method.
2. Description of the Related Art
As LSI has been recently fabricated in higher integration, there is an increasing need for a technique for fabricating a device in a smaller size. In particular, a minimum size for a wiring pattern is presently in an order of submicron, and hence, a need for fabricating a device in a smaller size has been increased.
One of techniques having been developed for meeting such a need is chemical mechanical polishing (hereinafter, referred to simply as "CMP"). CMP is presently indispensable for planarization of an interlayer insulating film, formation of a plug in a via-hole, and formation of a buried metal wiring layer, for instance.
FIGS. 1A to 1E illustrates steps of forming a buried metal wiring layer by CMP.
First, as illustrated in FIG. 1A, an insulating film 41 is formed on a semiconductor substrate 40. Then, the insulating film 41 is planarized.
Then, as illustrated in FIG. 1B, there are formed a plurality of recesses 42 at a surface of the insulating film 41 by photolithography and etching.
Then, as illustrated in FIG. 1C, a barrier metal film 43 is formed all over the insulating film 41.
Then, as illustrated in FIG. 1D, a metal film 44 for making a wiring layer is deposited on the barrier metal film 43.
Then, the metal film 44 and the barrier metal film 43 are polished by CMP so that the metal film 44 remains only in the recesses 42, as illustrated in FIG. 1E.
Thus, there is completed a wiring layer composed of the metal film 44.
FIG. 2A illustrates a step of forming a wiring layer composed of copper.
First, a silicon dioxide film 51 as an underlying oxide film is formed with recesses 52. Then, a titanium nitride (TiN) film 53 as a barrier film is formed all over the silicon dioxide film 51.
Then, a copper film 54 is formed on the TiN barrier film 53 by plating so that the recesses 52 are filled with the copper film 54.
Then, the copper film 54 is polished by CMP in which there is used slurry consisting of alumina particles and aqueous solution of hydrogen peroxide as an oxidizer.
The polishing conditions for polishing the copper film 54 are generally as follows.
Polishing load: 490 g/cm.sup.2 PA1 Linear velocity at a center of a wafer: 0.2 m/s PA1 Revolution per minute (rpm): 100 (100 rpm is equivalent to a linear velocity of 0.5 m/s) PA1 Load: 300 gf/cm.sup.2 PA1 Revolution per minute of a table: 30 to 60 rpm PA1 Load: 2 to 8 psi
However, if the copper film 54 is polished by CMP in the above-mentioned conditions, a mechanical force acts on the copper film 54 because the polishing load and the linear velocity are both relatively high, resulting in that the copper film 54 might be peeled off from the barrier film 53 after CMP has been carried out, as illustrated in FIG. 2B.
A lot of suggestion have been made about CMP, for instance, in Japanese Unexamined Patent Publications Nos. 7-86216, 7-193034, 9-22907, 9-213699, and 8-288389 (Japanese Patent No. 2728025).
Japanese Unexamined Patent Publication No. 7-86216 has suggested a method in which particles composed of organic polymer are used as polishing particles, and residual slurry is burnt for removal after CMP has been carried out. In this method, since the polishing particles are spherical ones, a film to be polished is not damaged. The polishing conditions in this method are as follows.
Japanese Unexamined Patent Publication No. 9-213699 has suggested a method of forming a multi-layered wiring structure, including the steps of filling recesses with aluminum by selective CVD, and polishing the aluminum by CMP. The polishing conditions are as follows.
30 to 60 rpm is equivalent to a linear velocity of 0.15 to 0.3 m/s, and 2 to 8 psi is equivalent to 140 to 560 gf/cm.sup.2.
The above-mentioned methods cannot avoid that a mechanical force acts on a copper film, and hence, a copper film is peeled off after CMP has been carried out, similarly to FIG. 2B, because a polishing load and a linear velocity are both relatively high in the polishing conditions in the above-mentioned methods.